1. STEMS
All plants begin their development as herbaceous i.e. non woody organisms. True woody plants in
due course grow into woody stems while those that do not produce woody stems, remain
herbaceous stems throughout their life span, in general, plants that die within one growing season
(annuals) have green herbaceous stems, and are usually monocots but many dicots also have
herbaceous stems. This paper discusses the three different types of stem structures; herbaceous
dicotyledonous stems, woody dicotyledonous stems and monocotyledonous stems.
HERBACEOUS DICOTYLEDONOUS STEMS
The tissues of these annual dicots are largely primary, although the cambium may produce some
secondary tissues (Stern, 2008). The vascular bundles of these herbaceous dicot stems are arranged
in a cylinder that separates the cortex from the pith, although in a few plants the xylem and the
phloem are produced as continuous rings (cylinders) instead of in separate bundles. These stems
are substantial but are not real wood, they rather filled with pith to give them rigidity and can be
annual, biennial or perennial.
Figure 1.0
WOODY DICOTYLEDONOUS STEMS
In the early stages of development, the primary tissues of stems of young herbaceous dicots and
woody dicots are all arranged in a similar pattern. In woody plants, however, obvious differences
begin to appear as soon as the vascular cambium and the cork cambium develop. The most
noticeable difference involve the development of secondary xylem in woody dicot stems, this
development of the secondary xylem leads into increase in diameter and thickening of the plant
stems. Some woody dicot stems in tropical trees (e.g. ebony), in which both the vascular cambium
and the cork cambium are active all year, produce a uniform wood that continues increasing in

2. diameter and thicken throughout its life span (Stern, 2008). There vascular bundles are arranged
in rings that are used to determine their age.
Figure 1.1
MONOCOTYLEDONOUS STEMS
Most monocots (e.g. grasses) are herbaceous plants that do not attain great size. These monocot
stems do not have a vascular cambium and cork cambium because of the absence of distinct areas
of cortex and pith; the parenchyma tissue is not divided and thus do not produce secondary vascular
tissues (Stern, 2008).There is an absence of a concentric ring of vascular tissue in these monocot
stems, instead, the xylem and phloem are distributed throughout the pith of the stem in discrete
vascular bundles, thus the xylem is closer to the center of the stem and phloem is closer to the
surface.
Figure 1.2

3. In summary, there are three different stem structures; herbaceous dicotyledonous stems which have
discrete vascular bundles arranged in cylinder appearing in narrow rings, woody dicotyledonous
stems which have vascular bundles in ring and monocotyledonous stems which have scattered
vascular bundles.

4. REFEERENCE
Stern, K., Bidlack, J. & Jansky, S. (2008). Introductory Plant Biology, 11th Ed. McGrawhill. New
York
Bell, P.R. & Woodcock C.L.K., (1983). The Diversity Of Green Plants, Edward Arnold,
Scortland.